Heat pipe

ABSTRACT

A heat pipe includes a casing and a plurality of wick layers. The casing has an inner wall. The wick layers stack at an inner surface of the casing in turn. The wick layers respectively define a plurality of pores therein. Diameters of the pores of each of the wick layers gradually decrease from the inner wall to center of the casing.

BACKGROUND

1. Technical Field

The present disclosure relates to heat transfer/dissipating device, and more particularly to a heat pipe.

2. Description of Related Art

Heat pipes have excellent heat transfer performance due to their low thermal resistance, and therefore are an effective means for heat transfer from heat sources. A heat pipe is usually a vacuum casing containing therein a working fluid, and a wick structure.

The primary function of a wick is to draw condensed liquid back to an evaporating section of a heat pipe under the capillary pressure developed thereby. Therefore, the capillary pressure is an important parameter affecting the performance of the wick. Since it is well recognized that the capillary pressure of a wick increases due to a decrease in pore size of the wick, the sintered powder wick generally has a capillary pressure larger than that of the other wicks due to its very dense structure of small particles. However, it is not always the best way to choose a dense wick with small-sized pores, because the flow resistance to the condensed liquid also increases due to a decrease in pore size of the wick. The increased flow resistance reduces the speed of the condensed liquid in returning to the evaporating section. As a result, a heat pipe with a wick that has too large or too small pore size often suffers dry-out problem at the evaporating section as the condensed liquid cannot be timely sent back to the evaporating section of the heat pipe.

Therefore, what is needed is a heat pipe which can overcome the above described shortcomings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinally cross-sectional view of a middle part of a heat pipe, in accordance with a first embodiment of the present disclosure.

FIG. 2 is a transversely cross-sectional view of the heat pipe, in accordance with the first embodiment of the present disclosure.

FIG. 3 is a transversely cross-sectional view of a heat pipe, in accordance with a second embodiment of the present disclosure.

FIG. 4 is a transversely cross-sectional view of a heat pipe, in accordance with a third embodiment of the present disclosure.

DETAILED DESCRIPTION

Referring to FIGS. 1 to 2, a heat pipe 100 according to a first embodiment of the present disclosure is shown. The heat pipe 100 includes a casing 10, a working liquid 20 received in the casing 10, and a wick structure assembly 30 arranged at an inner surface of the casing 10 and saturated with the working fluid 20. The casing 10 includes an evaporating section (not labeled) and a condensing section (not labeled) at respective opposite ends thereof.

The casing 10 is sealed and has a cylindrical shape. The casing 10 is typically made of high thermally conductive materials such as copper or copper alloys. The casing 10 defines a vacuum sealed chamber 50, which is employed to carry, under phase transitions between liquid state and vapor state, thermal energy from the evaporating section to the condensing section.

The wick structure assembly 30 has a multiple layer structure consisting of a plurality of wick layers 32 along a radial direction of the heat pipe 100. In the present embodiment, the wick structure assembly 30 includes eight wick layers 32 stacked at an inner surface of the casing 10 in sequence, and the wick layers 32 communicate with each other. The wick layers 32 respectively define a plurality of pores 320 therein. In the present embodiment, diameters of the pores 320 of the wick layers 32 gradually decrease from the inner wall to center of the casing 10. The wick layers 32 include a first wick layer 32 a adjacent to and connect to the inner wall of the casing 10, and a second wick layer 32 b near the center of the casing 10 and away from the inner wall of the casing 10. The first wick layer 32 a can be selected from one of groove-type wick layer, fine-mesh wick layer or sintered powder wick layer, and the other six wick layers 32 can be selected from sintered powder wick layer, or fine-mesh wick layer. In the present embodiment, the second wick layer 32 b is sintered powder wick layer, and the other six wick layers 32 are fine-mesh wick layer, and a porosity of all the wick layers 32 ranges from 40 to 65 percents.

In the present embodiment, diameters of the pores of the wick layers 32 gradually decrease from the inner wall to center of the casing 10, therefore, the heat pipe 100 has a relatively large capillary force and a relatively low flow resistance, so as to effectively and timely bring the condensed working liquid back from the condensing section to the evaporating section.

The working liquid 20 is received in the casing 10, and can flow from the condensing section to the evaporating section via capillary force provided by the wick structure assembly 30. The working liquid 20 at the evaporating section is heated and vaporized to the condensing section. The vaporized working fluid 20 exchanges heat at the condensing section and is condensed to liquid. The condensed working fluid 20 returns to the evaporating section via the wick structure assembly 30. The working liquid 20 can be selected from a group consisting of water, alcohol, ammonia and combination thereof.

It can be understood that an amount of wick layers 32 can be three, four, five, six or seven, and the second wick layer 32 b is sintered powder wick layer, and the other wick layer 32 are fine-mesh wick layers.

Referring to FIG. 3, a heat pipe 600 according to a second embodiment of the present disclosure is shown. Differing from the heat pipe 100 of the first embodiment, a wick structure assembly 60 of the heat pipe 600 includes a plurality of wick layers 62, and the wick layers 62 are groove-type wick layers and fine-mesh wick layers alternately stacked together. The wick layers 62 are communicated with each other, and diameters of the pores 620 of each of the wick layers 62 gradually decrease from the inner wall to center of the casing 10. In the present embodiment, the wick layers 62 include a first wick layer 621, a second wick layer 622, a third wick layer 623, a fourth wick layer 624, a fifth wick layer 625, a sixth wick layer 626, a seventh wick layer 627 and an eighth wick layer 628 stacked at an inner surface of the casing 10 in sequence, and along directions from the inner wall to center of the casing 10. The first, third, fifth and seventh wick layers 621, 623, 625, 627 are fine-mesh wick layers, and the second, fourth, sixth, and eighth wick layers 622, 624, 626, 628 are groove-type wick layers.

Referring to FIG. 4, a heat pipe 700 according to a third embodiment of the present disclosure is shown. Differing from the heat pipe 100, the wick layer assembly 70 includes a plurality of wick layers 72, and the wick layers 72 are fine-mesh wick layers and sintered powder wick layers alternately stacked together. The wick layers 72 are communicated with each other, and diameters of the pores 720 of each of the wick layers 72 gradually decrease from the inner wall to center of the casing 10. In the present embodiment, the wick layers 72 include a first wick layer 721, a second wick layer 722, a third wick layer 723, a fourth wick layer 724, a fifth wick layer 725, and a sixth wick layer 726 stacked at an inner surface of the casing 10 in turn, and along directions from the inner wall to center of the casing 10. The first, third, and fifth wick layers 721, 723, 7257 are fine-mesh wick layers, and the second, fourth, and sixth wick layers 722, 724, 726, 728 are sintered powder wick layers. It can be understood that the wick layer assembly 70 can be consist of four wick layers 72, and the four wick layers 72 are fine-mesh wick layers and sintered powder wick layers alternating with each other.

Following tables shows heat transfer performance of the wick layers 72 of the heat pipe 700 compared with that of the conventional heat pipe.

Average of the max load of heat Average of thermal Type Number transfer (W) resistance (° C./W) Conventional sintered 30 39.5 0.08 heat pipe The heat pipe of the 30 57.5 0.07 third embodiment (four wick layers) The heat pipe of the 30 58.9 0.08 third embodiment (six wick layers) Remark: 1: A height of the conventional sintered heat pipe when pressed is equal to that of the heat pipe of the third embodiment, both are 3.5 mm. 2: The working temperature is 50 Celsius degrees.

Average of the max load of heat Average of thermal Type Number transfer (W) resistance (° C./W) Conventional sintered 30 35.5 0.1 heat pipe The heat pipe of the 30 55.0 0.08 third embodiment (four wick layers) The heat pipe of the 30 54.3 0.1 third embodiment (six wick layers) Remark: 1, A height of the conventional sintered heat pipe when pressed is equal to that of the heat pipe of the third embodiment, both are 3.0 mm. 2, The working temperature is 50 Celsius degrees.

It can be concluded from the above tables, the heat pipe 700 has a smaller liquid resistance and greater capillary force than the conventional sintered heat pipe. In alternative embodiment, the heat pipes 100, 600, 700 can be elongated plate heat pipe, and the casing 10 can be rectangle shape, and an amount of the wick layers 32, 62, 72 can be three, four, five, six, seven or eight.

It is to be further understood that even though numerous characteristics and advantages have been set forth in the foregoing description of embodiments, together with details of the structures and functions of the embodiments, the disclosure is illustrative only; and that changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the disclosure to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed. 

1. A heat pipe comprising: a casing, the casing having an inner wall; and a plurality of wick layers stacked at an inner surface of the casing in turn, the wick layers respectively defining a plurality of pores therein, diameters of the pores of the wick layers gradually decreasing from the inner wall to a center of the casing.
 2. The heat pipe of claim 1, wherein the wick layers are more than three and less than eight.
 3. The heat pipe of claim 1, wherein the wick layers comprises a first wick layer adjacent to and connect to the inner wall of the casing, the first wick can be selected from groove-type wick layer, fine-mesh wick layer or sintered powder wick layer.
 4. The heat pipe of claim 1, wherein the wick layers comprises a second wick layer near a center of the casing and away from the inner wall of the casing, the inner wick being a sintered powder wick layer, and the others being a fine-mesh wick layer.
 5. The heat pipe of claim 1, wherein the wick layers are groove-type wick layers and fine-mesh wick layers alternating stacked together each other.
 6. The heat pipe of claim 5, wherein the wick layers comprise a first wick layer adjacent to and connect to the inner wall of the casing, the first wick layer being a fine-mesh wick layer.
 7. The heat pipe of claim 1, wherein the wick layers are fine-mesh wick layers and sintered powder wick layers alternating stacked together.
 8. The heat pipe of claim 7, wherein the wick layers comprise a first wick layer adjacent to and connect to the inner wall of the casing, the first wick layer being a fine-mesh wick layer.
 9. The heat pipe of claim 1, wherein a porosity of all the wick layers ranges from 40 to 65 percents.
 10. The heat pipe of claim 1, wherein wick layers are communicated with each other.
 11. A heat pipe comprising: a sealed cylindrical casing, the casing having an inner wall; and more than three wick layers stacked at an inner surface of the casing in turn, the wick layers respectively defining a plurality of pores therein, diameters of the pores of the wick layers gradually decreasing from the inner wall to center of the casing, and a porosity of all the wick layers ranging from 40 to 65 percents.
 12. The heat pipe of claim 11, wherein the wick layers comprises a second wick layer near a center of the casing and away from the inner wall of the casing, the inner wick being a sintered powder wick layer, and the others being a fine-mesh wick layer.
 13. The heat pipe of claim 11, wherein the wick layers are groove-type wick layers and fine-mesh wick layers alternating stacked together.
 14. The heat pipe of claim 11, wherein the wick layers are fine-mesh wick layers and sintered powder wick layers alternating stacked together. 